一、根据id查询课程发布信息

方式一：业务层组装多个表多次的查询结果
方式二：数据访问层进行关联查询
我们使用第二种方式实现

1、定义vo

package com.guli.edu.vo;
@ApiModel(value = "课程发布信息")
@Data
public class CoursePublishVo  implements Serializable {
    private static final long serialVersionUID = 1L;
    private String title;
    private String cover;
    private Integer lessonNum;
    private String subjectLevelOne;
    private String subjectLevelTwo;
    private String teacherName;
    private String price;//只用于显示
}

2、数据访问层

接口：CourseMapper.java

package com.guli.edu.mapper;
public interface CourseMapper extends BaseMapper<Course> {
    CoursePublishVo selectCoursePublishVoById(String id);
}

实现：CourseMapper.xml

<select id="getCoursePublishVoById" resultType="com.guli.edu.vo.CoursePublishVo">
    SELECT
        c.title,
        c.cover,
        c.lesson_num AS lessonNum,
        CONVERT(c.price, DECIMAL(8,2)) AS price,
        s1.title AS subjectLevelOne,
        s2.title AS subjectLevelTwo,
        t.name AS teacherName
    FROM
        edu_course c
        LEFT JOIN edu_teacher t ON c.teacher_id = t.id
        LEFT JOIN edu_subject s1 ON c.subject_parent_id = s1.id
        LEFT JOIN edu_subject s2 ON c.subject_id = s2.id
    WHERE
        c.id = #{id}
</select>

3、业务层

接口：CourseService.java

CoursePublishVo getCoursePublishVoById(String id);

实现：CourseServiceImpl.java

@Override
public CoursePublishVo getCoursePublishVoById(String id) {
    return baseMapper.getCoursePublishVoById(id);
}

4、web层

@ApiOperation(value = "根据ID获取课程发布信息")
@GetMapping("course-publish-info/{id}")
public R getCoursePublishVoById(
    @ApiParam(name = "id", value = "课程ID", required = true)
    @PathVariable String id){
    CoursePublishVo courseInfoForm = courseService.getCoursePublishVoById(id);
    return R.ok().data("item", courseInfoForm);
}

测试：报告异常
AbstractHandlerExceptionResolver.java:194 |org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver |Resolved exception caused by handler execution: org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.guli.edu.mapper.CourseMapper.getCoursePublishVoById

问题分析：
dao层编译后只有class文件，没有mapper.xml，因为maven工程在默认情况下src/main/java目录下的所有资源文件是不发布到target目录下的，

解决方案：
1、在guli_edu的pom中配置如下节点

<!-- 项目打包时会将java目录中的*.xml文件也进行打包 -->
<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
    </resources>
</build>

重新打包项目会发现target目录下出现了xml文件夹

2、在Spring Boot配置文件中添加配置

#配置mapper xml文件的路径
mybatis-plus.mapper-locations=classpath:com/guli/edu/mapper/xml/*.xml

二、根据id发布课程

1、web层

@ApiOperation(value = "根据id发布课程")
@PutMapping("publish-course/{id}")
public R publishCourseById(
    @ApiParam(name = "id", value = "课程ID", required = true)
    @PathVariable String id){
    courseService.publishCourseById(id);
    return R.ok();
}

2、service层

接口

void publishCourseById(String id);

实现

@Override
public boolean publishCourseById(String id) {
    Course course = new Course();
    course.setId(id);
    course.setStatus(Course.COURSE_NORMAL);
    Integer count = baseMapper.updateById(course);
    return null != count && count > 0;
}